Unlike silver generally used in real life, chemical, physical, and optical properties of nano-sized silver particles are significantly different from each other according to a shape and a size, and unexpected properties may be exhibited. Therefore, silver nanoparticles have proven to be highly efficient in various fields such as a sensor, a catalyst, an electronic circuit, photonics, and the like, by using properties of the silver nanoparticles.
A most important factor for using and commercializing the silver nanoparticles as described above is synthesis of particles having a uniform shape and size. Methods for synthesizing silver nanoparticles in a liquid phase have been widely known. The methods may be roughly divided into a method of synthesizing silver nanoparticles in a hydrophilic solvent and a method of synthesizing silver nanoparticles in a hydrophobic solvent.
More specifically, in the method of synthesizing silver nanoparticles in a hydrophilic solvent, water or alcohol is mainly used as the solvent, and an oxidized silver precursor is reduced using NaXH4 (X=B or Al), hydrazine, or the like, which is a strong reducing agent. In the method of synthesizing silver nanoparticles in a hydrophilic solvent, there are various limitations in view of mass-production, non-uniform shape and sizes, and the like.
In order to solve the problems as described above, many researchers developed a method of synthesizing uniform silver nanoparticles in a hydrophobic solvent. A method of mixing a paraffin solvent, a silver precursor, and an amine molecule serving as a surfactant and a reducing agent, or a molecule containing two or more hydroxyl groups corresponding to a separate reducing agent with each other and inducing a chemical reaction for nanoparticles has been mainly used. Uniform silver nanoparticles may be synthesized through the chemical reaction in this hydrophobic solvent, but in a process of dissolving the silver precursor, which is hydrophilic, nanoparticles are partially already formed, such that non-uniform nanoparticles may be formed.
For example, a method of synthesizing silver nanoparticles having a size of 1 to 40 nm by using a silver precursor, a heterogeneous metal precursor, and alkyl amine has been disclosed in Korean Patent Laid-Open Publication No. 10-2009-0012605. However, in this method, dissociation and reduction reactions are carried out at a single temperature of 150° C. or less, such that size uniformity of the silver nanoparticles may be slightly deteriorated.
That is, the methods known in the art have problems in view of uniformity and reproducibility. Therefore, in order to synthesize significantly uniform silver nanoparticles on a large scale, a method capable of synthesizing silver nanoparticles through a simple synthesis process, having reproducibility, and satisfying a low cost synthesis should be developed.